This invention relates generally to turbine engines, and more particularly, to slot cooled ring combustors for turbine engines.
A turbine engine includes a compressor for compressing air which is suitably mixed with a fuel and channeled to a combustor wherein the mixture is ignited for generating hot combustion gases. The gases are channeled to a turbine, which extracts energy from the combustion gases for powering the compressor, as well as producing useful work for propelling an aircraft in flight and for powering a load, such as an electrical generator. Increased efficiency in gas turbine engines is accomplished at least in part by an increase in the operating temperature of the combustor. A principal limitation on the operating combustor temperature has been material limitations of a liner in the combustor.
One effective technique for cooling the combustor liner is thin film convection cooling wherein a protective film boundary of cool air flows along an inner surface of the liner via air cooling slots to insulate the liner from hot combustion gases. Aside from forming a protective boundary between the liner and hot gases, the cooling air allows for convective cooling of the liner. See, for example, U.S. Pat. No. 4,259,842. However, the air slots tend to encourage turbulence of combustion gases separating off the ends of the slots, which increases a heat transfer coefficient on the ends of the slots and hence increases the heat load on the combustor liner.
Another effective technique for cooling a combustor liner thermal barrier is the use of thermal barrier coatings that are applied to the inner surface of a combustor liner for providing thermal insulation against combustion gases. Thermal barrier coatings reduce the amount of cooling air required for a given combustion gas temperature, or allow an increase in a combustion gas temperature for increasing efficiency of the engine. See, for example, U.S. Pat. No. 5,960,632. However, process limitations for applying thermal barrier coating, namely undesirable buildup of thermal barrier coatings, prevent thermal barrier coating from being applied to rear facing edges of the combustor liner, thereby exposing the edges to hot combustion gases and allowing undesirable heat flow into the liner.
Accordingly, it would be desirable to provide a combuster assembly with rear facing edges that may be thermal barrier coated without creating undesirable heat buildup in air cooling slots, that reduce combustion gas turbulence at each rear facing edge, and that reduce the combustor liner surface area of the overhang portions.
In an exemplary embodiment of the invention, a combuster includes a combustor liner including a stepped combustor liner surface and at least one overhang portion forming an air cooling slot. A rear facing edge of the overhang portion is contoured to reduce turbulence of combustion gas flow and to reduce an exposed combustor liner surface of the overhang portion. A thermal barrier coating is applied to the contoured rear facing edge, further reducing heat flow into the overhang portion and lowering the operating temperature of the combustor. Thus, the amount of required air cooling is reduced, which can reduce exhaust emissions, increase engine performance, and extend a working life of the combustor assembly. In addition, because of the thermal barrier coating, higher combustion gas temperatures may be achieved to increase the efficiency of a turbine engine without having adverse effects on combustor assembly materials.